[LDC] PGO: Avoid COMDAT members with private linkage for Windows

To prevent according IR verifier errors with IR-based PGO ('comdat
global value has private linkage').

Author: kinke

llvm/lib/ProfileData/InstrProf.cpp

@@ -323,8 +323,13 @@ GlobalVariable *createPGOFuncNameVar(Module &M,
   else if (Linkage == GlobalValue::AvailableExternallyLinkage)
     Linkage = GlobalValue::LinkOnceODRLinkage;
   else if (Linkage == GlobalValue::InternalLinkage ||
-           Linkage == GlobalValue::ExternalLinkage)
-    Linkage = GlobalValue::PrivateLinkage;
+           Linkage == GlobalValue::ExternalLinkage) {
+    // LDC: use internal instead of private linkage for COFF (still local, but
+    //      allows for COMDATs on Windows)
+    Linkage = Triple(M.getTargetTriple()).isOSBinFormatCOFF()
+                  ? GlobalValue::InternalLinkage
+                  : GlobalValue::PrivateLinkage;
+  }
 
   auto *Value =
       ConstantDataArray::getString(M.getContext(), PGOFuncName, false);